Linear motion guide units have been extensively used in recent years with installed in the relatively sliding parts in machinery including machine tools, assembling machines, conveyors, and so on. In machine tools, especially, the linear motion guide units sometimes are needed to work with high accuracy on any tilted surface of the base or machine bed. Most advanced machines, moreover, seek for the linear motion guide units with no lubricant leakage to make them better for the environment and also improved to make lubrication more effectively with only a minor amount of lubricant.
In commonly-assigned Japanese Laid-Open Utility Model Application H06-35 645, a linear rolling-motion guide unit is disclosed in which flow-regulator valves are provided in lubricant grooves cut in the end caps to supply the lubricant equally in amount to both the load-carrying races spaced widthwise away from one another to the right and left in the slider, thereby ensuring better lubrication even if the linear motion guide unit works in any posture other than the horizontal. Nevertheless, the prior linear motion guide unit recited earlier, because of the construction the lubricant was led through the lubricant grooves cut directly into the end caps, was likely to incur any intermittent lubrication especially when the applied lubricant was minuscule or paltry in quantity, for example, as small as 0.03 cc per every twelve minutes. This made it even tougher to ensure the desired amount of lubricant to the load-carrying races in the circulating circuits, which allow the rolling elements to roll through there.
Another linear motion guide unit is disclosed in Japanese Laid-Open Patent Application 2005-155 909, which is constructed in a fashion to make it possible to apply the lubricant from any one of the front and sides of the end cans without causing lubricant leakage as well as accompanying any increase in production cost. In the construction as stated earlier, lubricant groove-formative members are each installed within the end caps that are mounted on the forward and aft ends in the moving direction of the slider. On the lubricant groove-formative members, there are made the lubricant grooves in a way to make it possible to supply the lubricant from any one of the front and sides of the end caps. With the prior linear motion guide unit recited earlier, however, special consideration must be taken that the lubricant does not leak out creep, especially when the applied lubricant is minuscule in quantity. To cope with this, the sealing means used to prevent lubricant leakage from the passages of lubricant flow would inevitably become sophisticated in construction.
Meanwhile, recently advanced machines and instruments including machine tools, and so on look to the development of the linear motion guide unit that can meet all the duties of high-speed sliding performance, high mechanical stiffness, and high accuracy while making it possible to ensure steady lubrication to the circulating circuits for the rolling elements in every working conditions including a tilted posture, another posture lying on its side, and so on even minor quantity of lubricant recommended in an aspect of lessening the environmental impact of lubricant. With the linear motion guide units in which the sliders are allowed to travel lengthwise of the elongated guide rail by virtue of more than one rolling element, positive application of lubricant to the load-carrying races defined between the raceway surfaces to carry the rolling elements through there is of course inevitable to continue maintaining an adequate lubricant film between the load-carrying races and the rolling elements to keep them against metal-to-metal contact that might otherwise occur abnormal wear and scuffing. Of two members of the class of linear motion guide units one of which has balls and the other has cylindrical rollers, the linear motion guide unit in which cylindrical rollers are selected as the rolling elements is preferable for the machine tools in aspects of heavy load-carrying capacity and moderate alignment accuracy. Thus, it remains a major challenge to develop any linear motion guide unit that might meet functional demands as stated earlier.